Valve-controlled internal combustion engines have one or multiple controllable inlet and outlet valves per cylinder. Variable valve drives permit a flexible activation of the valves in order to vary the opening time, closing time and/or the valve lift. In this way, the engine operation can be adapted for example to a specific load situation. For example, a variable valve drive can be realized by means of a so-called sliding cam system.
DE 196 11 641 C1 has disclosed an example of a sliding cam system of the type, by means of which the actuation of a gas exchange valve with multiple different lift curves is made possible. For this purpose, a sliding cam with at least one cam portion which has multiple cam tracks is mounted rotationally conjointly but axially displaceably on the camshaft, which sliding cam has a lift contour into which an actuator in the form of a pin is inserted from radially outside in order to generate an axial displacement of the sliding cam. By means of the axial displacement of the sliding cam, a different valve lift is set at the respective gas exchange valve. The sliding cam, after the axial displacement thereof relative to the camshaft, is thereby locked in its axial relative position on the camshaft.
DE 10 2011 050 484 A1 has disclosed an internal combustion engine with multiple cylinders, a cylinder head and a cylinder head cover. For the actuation of gas exchange valves, at least one rotatably mounted camshaft with at least one sliding cam which is axially displaceable on the respective camshaft is provided. The respective sliding cam has at least one slotted-guide portion with at least one groove. An actuator is provided for effecting an axial displacement of the respective sliding cam. The actuator is mounted in the cylinder head or in the cylinder head cover.
A disadvantage of known systems may be that, in the event of a failure of an actuator, no axial displacement of the sliding cam in accordance with the axial displacement assigned to the failed actuator is possible. Under some circumstances, it is thus no longer possible for the valve timings of the gas exchange valves to be varied. In a particularly adverse situation, it is for example then not possible for a gas exchange valve which is being operated in an engine braking mode by means of the sliding cam system to be switched back to a normal mode.